1. Field of the Invention
The present invention relates to a method for producing a semiconductor epitaxial wafer having an epitaxial growth layer on a silicon-based substrate and to a semiconductor epitaxial wafer.
2. Description of the Related Art
In order to produce a semiconductor epitaxial wafer, epitaxial growth is performed on the front surface of a silicon-based substrate (for example, a silicon substrate or a silicon carbide substrate) or the like by using a commercially available epitaxial production apparatus, whereby a hetero-homo epitaxial wafer is produced.
In an epitaxial wafer having an epitaxial growth layer composed of a nitride semiconductor, the epitaxial growth layer disposed on a silicon-based substrate, the film thickness of the epitaxial growth layer increases on the outer edge portion and a crown (a projection protruding from the main surface of the growth layer) in the epitaxial growth layer appears.
Conditions such as the thickness of each layer of the epitaxial growth layer are selected such that warpage of the silicon-based substrate and stress in the epitaxial growth layer are optimized in a central part of a wafer which is used as a semiconductor device. As a result, if the crown appears, the balance between the stress produced in the epitaxial growth layer and the warpage of the substrate is lost, which affects the epitaxial growth layer and causes hexagonal patterned cracks or the like to appear in the epitaxial growth layer near the outer edge portion.
In order to prevent the appearance of such a crown, a method of, for example, chamfering the outer edge portion of a silicon-based substrate and forming an epitaxial growth layer thereon is proposed (for example, Patent Literature 1).
Moreover, as measures against cracks, performing epitaxial growth after roughening the surface near a Si substrate edge (Patent Literature 2), using, as a substrate for hetero epitaxial growth, a silicon substrate whose principal surface is the (111) plane having orientation flat in a direction obtained by rotating the <110> direction at an angle of 30°, 90°, or 150° in a counterclockwise direction by using the <111> direction as a rotation axis (Patent Literature 3), performing epitaxial growth in a state in which the periphery portion of a silicon-based substrate is covered with a ring (Patent Literature 4), and so forth are proposed.
Furthermore, in an epitaxial wafer having a GaN layer and an AlN layer epitaxially grown on a silicon substrate, if a crack appears at the edge portion of the wafer during epitaxial growth, gas of TMA (trimethylaluminum) or TMG (trimethylgallium) which is the source gas enters through an opening of the crack and reacts with Si, whereby a reaction mark appears.
As measures against such a reaction mark, growing a thick GaN film epitaxially on a SOI substrate via a buffer film (an AlN film) is proposed (Patent Literature 5).